This invention relates generally to self-emitting color display devices such as color cathode ray tubes (CRTs) and is particularly directed to a black surface coating for the display screen of a color CRT for providing a high level of video image contrast while affording uniform light absorbance over the entire visible spectrum for improved color video image presentation.
Self-emitting display devices, such as of the CRT-type, produce a video image by the bombardment of phosphor elements disposed on the inner surface of the device""s display screen by high energy electrons. In a color display device, the phosphor elements are separated into three groups, with each group emitting one of the primary colors of red, green or blue when impinged upon by the energetic electrons.
Typically disposed on the outer surface of the device""s display screen is a two-layer coating in the form of an inner antistatic layer and an outer antireflective layer containing silica. The inner antistatic layer typically includes electrically conductive carbon black particles, but may also include antimony-doped tin oxide or indium-doped tin oxide. The electrically conductive antistatic layer provides electrostatic shielding for the display device as well as grounding of electrostatic charge which tends to build-up on the display screen. The carbon black particles also absorb light nonuniformily over the visible spectrum. In particular, the carbon black particles absorb more blue light having a wavelength in the range of 400-500 nm than light of other wavelengths in the visible spectrum. Absorption of blue light by the carbon black particles in the antistatic layer gives rise to a color video image having a yellowish tint. This detracts from the appearance of the video image because of poor color purity.
The present invention addresses the aforementioned limitations of the prior art by providing a coating for the outer surface of a video display screen having electrically conductive carbon black particles as well as a blue pigment, or dye, to provide a xe2x80x9cpure blackxe2x80x9d layer which is characterized by uniform light absorbance over the entire visible spectrum for improved video image presentation.
Accordingly, it is an object of the present invention to provide an optical coating for the outer surface of a cathode ray tube (CRT) display screen having improved light absorption characteristics.
Another object of the present invention to provide a carbon black-based coating for a CRT display screen having uniform light absorption characteristics over the entire visible spectrum for improved color video image presentation.
Yet another object of the present invention is to provide a CRT display screen coating containing carbon black particles and further incorporating a blue pigment, or dye, to compensate for increased blue light absorption by the carbon black to provide uniform color absorption over the entire visible spectrum for improved video image color purity.
A further object of the present invention is to provide an improved color video image on the display screen of a self-emitting display device by permanently affixing an electrically conductive color filter on the outer surface of the device""s display screen which absorbs light uniformly over the entire visible spectrum.
The present invention contemplates an electrically conductive coating for an outer surface of a glass display screen of a self-emitting display device, wherein the glass display screen further includes a phosphor coating on an inner surface thereof, and wherein the phosphor coating is responsive to energetic electrons incident thereon for providing a video image, the coating comprising: a thin layer of carbon black solution having a black appearance and disposed on the outer surface of the device""s glass display screen; and a blue additive in the carbon black solution to reduce absorbance of blue light by the carbon black and provide substantially uniform color absorption by the carbon black solution over the visible light spectrum.